Various techniques have been developed for the automated mounting of electronic components to printed circuit boards (PCB's). During mounting, substantial forces can be exerted on the PCB by the automated placement head. Accordingly, assembly processing requires back side support of a chosen substrate, such as a circuit board, capable of withstanding such forces. The back side support should provide good, solid support for allowing even and accurate placement of components on the top side of the substrate. Good support is needed where fine-pitched component leads are being placed. The support, however, should also avoid damaging components on the back side of the PCB where a double-sided board is used. Further, evenly distributed support under the placement area assists in avoiding the cracking of solder joints or the breaking of component leads from existing solder joints. This result can occur to previously placed components on the back side of the board, as components on the top side of the board are affixed, if the support is not proper.
One apparatus and method for supporting the back side of a PCB is disclosed in U.S. Pat. No. 5,820,117 (Thompson, et. al.). Here, an air bladder fixture tooling for supporting circuit board assembly processing is detailed. The bladder is positioned below the circuit board within a containment unit adapted for use with conventional railed assembly equipment. While the air bladder may provide uniform back side support, the PCB is not dissuaded from moving, bulging, bending or bowing away from contact with the bladder, especially at those locations distant from the slotted, opposing rails. Therefore, the PCB does not remain in contact with the bladder during component head placement.
Further, the bladder in Thompson is limited to a sole air compartment or chamber. Thus, it can be expected that some portions of the bladder, especially those furthest from the side walls, will “balloon” as the air bladder is inflated. As a result, the support provided by the air bladder furthest from the side walls can be greater than the support provided proximate the side walls of the bladder. Among other drawbacks, support provided by the bladder can be uneven and cause injury to the PCB or components. Also, with a sole chamber, Thompson is limited to a single internal pressure within the air bladder.
Given these limitations of the prior art, there is a clear need for an improved PCB support apparatus and method that overcomes such problems.